Sipes are commonly provided in a tread surface to enhance water absorption in order to enhance traveling performance on wet road surfaces and icy and snowy road surfaces. However, if an excessive number of sipes are disposed in the tread surface, tread rigidity will decline, leading to steering stability and braking ability being negatively affected. Therefore, conventionally, various technologies have been proposed regarding the form and arrangement of sipes (e.g. see Japanese Unexamined Patent Application No. H08-276709A).
Of these proposals, Japanese Unexamined Patent Application No. H08-276709A describes obtaining high gripping force and shearing rigidity on all road surfaces by disposing multiple sipes closely to each other in a tread surface where a planar form of the sipes is an “I” shape or a “Y” shape and an end of a cut has a round shape. However, with this proposal, it is difficult to ensure tread rigidity due to a disposal spacing of the sipes being excessively narrow and, even if the disposal spacing of the sipes is increased, because the width of the cuts of the sipes is formed equally with respect to the longitudinal direction, when the tread surface contacts the ground, the sipes will not open sufficiently, leading to the water absorption effect of the sipes being limited.